If a ship sailing with the wind such as a yacht is sailed, a crew has to steer the yacht with a target position and a wind direction taken into consideration. For example, in an upwind state, that is, where a target position (hereinafter, arbitrarily referred to as a “mark”) is on the windward side, the yacht cannot be sailed along the wind axis linearly, and must be sailed at a shallow angle as much as possible to the wind axis as disclosed in Magazine “KAZI,” KAZI Co., Ltd., published Oct. 1, 2008, pp. 110-115, 168-171. At this time, an angle at which the yacht can steer most in the direction of the target position is inherent to the respective yachts, and the angle is referred to as a maximum windward angle, which is 45 degrees, for example. Since the course direction is different from the direction of the target position, unless the yacht is sailed with tacking, it cannot arrive at the target position.
Meanwhile, not limited to a race, especially in the case of a race, a ship needs to be sailed with losses kept to a minimum in order to arrive at the target position earlier than other ships. For this purpose, the ship needs to always be sailed at the maximum windward angle described above, and even if the ship is always sailed at the maximum windward angle, it must be sailed in an area with a small sailing loss in order to arrive efficiently at the target position. Thus, the boundary of the area having a small sailing loss is a so called “layline.”
FIGS. 8A to 8C are diagrams for illustrating the layline and a concept of the loss during sailing. FIG. 8A shows a case where a wind blows from a mark 3 as a target point to a start line 2. FIGS. 8B and 8C show cases where the wind direction is changed under the situation of FIG. 8A. As shown in FIGS. 8A to 8C, a layline 4 is a virtual line extending in the direction at a maximum windward angle θup to the wind axis.
In a case in which a yacht 1 starts from the start line 2 to sail toward the mark 3, it can take various courses such as routes A to D shown in FIG. 8A, for example. However, if the course of the route C is taken, the yacht 1 enters an area on the windward side of an area surrounded by the layline 4. In this case, the sailing distance becomes longer compared with other routes (routes A, B and D), and a sailing loss occurs.
Further, as shown in FIGS. 8B and 8C, the wind does not blow constantly from one direction, and the wind direction and the wind speed change constantly. If the wind direction (wind axis) changes, the layline also changes, and as shown in FIGS. 8B and 8C, depending on the direction to which the wind direction (wind axis) changes, sailing until the target position is decided whether or not to be good.
For this reason, the crew must perform steering at each point under a situation momentarily changing while concerning the layline based on a relationship between the mark (target position) and a position of the crew's ship, and the wind direction, and estimating a change in the wind. Various information as a criterion for crew's judgment has been sensed by the crew, and the crew have been allowed to accurately perform sailing by repeating such experiences. That is, accurate sailing has not been able to be performed without knowledge, experience and concentration of the crew.